Here is the abstract for an article reporting on LINE L1 pseudogenes possibly moving around in neuronal precursors. I thought it was interesting. Don't know if I can set a link to the full article.
"Nature. 2005 Jun 16;435(7044):903-10.
Nature. 2005 Jun 16;435(7044):890-1.
Somatic mosaicism in neuronal precursor cells mediated by L1 retrotransposition.
Muotri AR, Chu VT, Marchetto MC, Deng W, Moran JV, Gage FH.
Laboratory of Genetics, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA.
Revealing the mechanisms for neuronal somatic diversification remains a central challenge for understanding individual differences in brain organization and function. Here we show that an engineered human LINE-1 (for long interspersed nuclear element-1; also known as L1) element can retrotranspose in neuronal precursors derived from rat hippocampus neural stem cells. The resulting retrotransposition events can alter the expression of neuronal genes, which, in turn, can influence neuronal cell fate in vitro. We further show that retrotransposition of a human L1 in transgenic mice results in neuronal somatic mosaicism. The molecular mechanism of action is probably mediated through Sox2, because a decrease in Sox2 expression during the early stages of neuronal differentiation is correlated with increases in both L1 transcription and retrotransposition. Our data therefore indicate that neuronal genomes might not be static, but some might be mosaic because of de novo L1 retrotransposition events."
Anyway, some trivia I know about LINE L1 is that they are enriched about 2x on the X chromosome and 3x on the Y compared to the rest of the genome. Most of them are degenerated (inactive) copies of reverse transcriptases but a few copies may be fully functional endogenous reverse transcriptases.
The somatic mosaicism that could result in daughter cells from an earlier retroposition event in a precursor is suggestive of lesion sites to me.